So What Is Giant Magnetoresistance?

SOURCE: Gary J. Wood via flickr

The news hook for the announcement of the winners of this year’s Nobel Prize in physics is easy: Giant Magnetoresistance expanded hard drive capacities to enable the miniaturization of the digital revolution, such as your iPod. But as coverage brews for the rest of the week, it’s worth looking at news stories that dig deeper into the science because they underscore the value of fundamental scientific research for society at large.

Albert Fert of the University of Paris-South in France and Peter Grünberg of Jülich Research Centre in Germany will share the prize for their 1988 discovery of giant magnetoresistance, or GMR in physics parlance. The Nobel committee’s scientific backgrounder on GMR notes in its conclusion that, “GMR is a good example of how an unexpected fundamental scientific discovery can quickly give rise to new technologies and commercial products,” which is a strong argument for both public and private support of basic research. The AFP story also notes that GMR can “be considered one of the first real applications of the promising field of nanotechnology.”

The basic GMR summary, from AFP and the AP, is that “very weak changes in magnetism generate larger changes in electrical resistance.” Reuters introduces electron spin, and all three explain that discovery of the principle allowed engineers to shrink hard drives by enabling detection of faint magnetic fluctuations as electrons pass through the layers of smaller and smaller hard discs. AP and the Reuters factbook note that since 1997, all hard drive reader heads rely on the effect.

Those are all accurate descriptions as far as they go, but it is understandably difficult to explain GMR and its implications for computer technology in one paragraph. Nature News takes three:

At the heart of GMR are the spins of electrons, which generate a magnetic field and can be aligned either up or down. An electron can easily pass through a material whose electrons are similarly aligned, but will encounter resistance when it passes through one with electrons aligned in the opposite direction.

Fert and Grünberg discovered the effect independently of each other using multiple layers of magnetic and non-magnetic materials only tens of nanometres thick. When all the layers were aligned in the same direction, say ‘up’, electrons with the same alignment passed through the material easily, whereas those with the opposite alignment struggled. But when the layers were organized in an alternating ‘up-down’ alignment, all electrons encountered resistance. The net effect was a rise in resistance that was much bigger than any seen before — hence ‘giant’.

This led to devices that are very sensitive to tiny magnetic fields. A hard disc drive stores bits on its surface as a pattern of magnetic fields. Until the discovery of GMR, hard discs used metal induction coils to read out the data. But the laws of induction meant that the coils, and thus the bits, had to be quite large. GMR opened up a way to build much smaller magnetic heads, says Claude Chappert of the University of Paris-South. The discovery revolutionized consumer electronics. “I think this triggered the common use of MP3 players,” he notes.

IBM capitalized on the GMR effect and explains their application of it on their research site—where you can also watch a detailed animation explaining how a hard drive reader head works (Via the first comment on Uncertain Principles).

Coverage of Nobel announcements necessitates rapid “science event” coverage, as Richard Lempert might note, rather than detailed scientific reporting. Getting into the technical weeds might obscure another more important point: Many consider this a well-deserved medal because it’s a perfect instance of basic research yielding near-term technological advancement. Moreover, the Nobels are a regular event that can reinforce public respect for scientists, which in turn becomes an opportunity to knit basic science, economically-empowering innovation, and public scientific literacy together. Nature News wins the prize.

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